Formation of Lattice Vacancies and their Effects on Lithium-ion Transport in LiBO2 Crystals: Comparative Ab Initio Studies

Abstract

The monoclinic (m-LBO) and tetragonal (t-LBO) polymorphs of the lithium metaborate (LiBO₂) material have significant potentials for technological applications such as solid electrolytes and electrode coatings of lithium-ion batteries. While comparative studies of electronic, ionic, and photonic properties in these polymorphs exist, the role of lattice vacancies on lithium-ion transport in these polymorphs remains unclear. In this study, we employed density functional theory (DFT) to investigate the formation of lattice vacancies and their impacts on the lattice structure, electronic properties, and lithium-ion migration energy barrier (E_m) in both m-LBO and t-LBO. Our DFT results reveal that boron and oxygen vacancies affect the lithium-ion transport in both the polymorphs, but in different ways. While oxygen vacancies lower E_m in m-LBO, they increase it in t-LBO. In contrast, boron vacancies significantly reduce E_m in both m-LBO and t-LBO, leading to a remarkably-enhanced ionic conductivity in both the polymorphs. This enhancement in the ionic conductivity could be due to favorable alterations in the crystal and electronic structures caused by the presence of boron vacancies. This improvement suggests a potential strategy for improving the ionic conductivity of the LiBO₂ material through boron vacancy generation. For example, boron vacancies might be created in the lattice structures of the LiBO₂ material using a controlled neutron irradiation.